A novel immunosuppressive strategy is being evaluated in renal transplant recipients at the University of Wisconsin. The regimen consists of induction therapy with two doses of Campath-1H, and anti-CD52 monoclonal antibody, two doses of steroid as pretreatment for Campath-1H, and subsequent maintenance monotherapy with rapamycin (Campath/Rapa). This regimen is substantially different from conventional immunosuppressive therapy for renal transplantation in that no maintenance steroids are used, no calcineurin inhibitors are used, and Campath-1H causes more profound depletion of lymphocytes than previously used antibodies in clinical transplantation such as antithymocyte globulin or OKT3. This new regimen appears promising for short-term results in that acute rejection has been completely avoided in five of five patients treated to date, and may have the additional benefit of preventing chronic rejection. The mechanistic studies proposed in this grant are aimed at answering three questions about the patients in this clinical trial: (1) what are the underlying mechanisms by which this regimen produces T-cell unresponsiveness in the patients? (2) would the in vitro tests suggest that these patients are tolerant such that they could be potentially removed form maintenance rapamycin therapy and (3) is chronic rejection prevented by this regimen? We propose to address these three questions using (1) the trans-vivo delayed-type hypersensitivity (DTH) assay which in both nonhuman primates and humans appears to correlate with rejection and tolerance, (2) study of the repopulating T-cell repertoire and function using Campath/Rapa, and (3) serial biopsies to assess chronic rejection in parallel with genetic analysis of matrix-associated genes as correlates of chronic allograft nephropathy (CAN). The first two specific aims will test whether T cells become anergic, if they develop regulatory function, if TGFbeta medicates regulation, whether the full T-cell repertoire recovers, and if T-cell signaling is modified in study patients. The third specific aim focuses on whether surrogate genetic markers of CAN can be identified by looking specifically at matrix-associated gene expression in renal allograft biopsies and peripheral blood mononuclear cells. This data will be correlated with histopathology of protocol biopsies.